French Patent No. 82.19842 (2 536 733) describes an automatic hydraulic balancing device for the jib of a crane in which a hydraulic jack chamber controlling the movement of the auxiliary arm of the jib and a chamber of the hydraulic jack controlling the counterweight balancing beam are connected together in series, while the other chamber of each of the two jacks is selectively connected using a hydraulic distributor either to a hydraulic fluid supply source, or to a hydraulic fluid reservoir. The result is that fluid is transferred into the balancing line between the two jacks, causing automatic balancing of the jib by proportional displacements of the centres of gravity of the auxiliary arm and the counterweight.
This known device enjoys deserved success, however, it does have the disadvantage that due to leaks that occur in hydraulic circuits, particularly at seals, there may be a lack of synchronisation in the movements of the auxiliary arm and the counterweight balancing beam which can disturb operation of the device.